Igniter plug

ABSTRACT

An igniter plug for a turbine engine capable of operating at high temperatures without failure of internal insulators that separate the main electrode from the ground electrode. The igniter plug includes an internal spring (100 or 200) that allows a forward insulator (80) to move in response to thermal expansion and contraction and to continually forwardly bias the insulator (80) against the front portion of the ground electrode (20) so that the insulator (80) is always in pressure contact with the forward end of the ground electrode (20).

' D United States Patent 1191 [111 3,882,338 Meyer 1 1 May 6, 1975 IGNITER PLUG 2.459286 1 1949 Rabezzana et a1 .1 313/1 1.5 n en or: He u P. Meyer, Sidney NY 3.745.400 7/1973 Meyer 313/144 [73] Assignee: The Bendix Corporation, Southfield, Primary E j A|fld L Brody MlCh. Attorney, Agent, or FirmRaymond J. Eifler [22] Filed: Jan. 16, 1974 211 Appl No: 433,944 1571 ABSTRACT An igniter plug for a turbine engine capable of operats Cl. 4 I I 1 v I u at temperatures without failure Of internal in- 3l3/l4l'. 313/143 sulators that separate the main electrode from the [5]] Int. Cl. N H0 13/20. 6 13/24 ground electrode. The igniter plug includes an internal [53] Field of Search 313/ 144 spring (100 or 200) that allows a forward insulator 313/126 127 123/169:- L (80) to move in response to thermal expansion and v a 1 1 contraction and to continually forwardly bias the insu later (80) against the front portion of the ground elec- [561 References Cited trode (20) so that the insulator (80) is always in pressure contact with the forward end of the ground elec- UNITED STATES PATENTS node (20) 1 525,4l5 2/1925 Seibert 1. 313/127 X 2,025,914 12/1235 Tetlow .1 313/137 8 Claims, 1 Drawing Figure 'x j n n 7 22 \Y F- M te I f Y VH w 52 3/ X" 1 /a Y 1/ /Ii I I." j 'v 2/ /77% I 20 (10 IGNITER PLUG BACKGROUND OF THE INVENTION This invention relates to a spark discharge device for igniting combustible materials and more particularly to an improved igniter plug for igniting fuel in a turbine engine. The invention is most particuarly related to a novel biasing arrangement that acts upon the insulator that separates the main electrode from the ground electrode at the front end of the igniter plug.

Igniter plugs generally comprise a metal shell or body that has a flange or other mounting means for mounting the igniter plug in a turbine engine. the shell constituting one electrode of the igniter plug. A central electrode passes through the shell and is supported within the shell by an insulator which surrounds the central electrode and which is fitted into an opening in the metal shell. A copper packing ring or bushing is then provided between the insulator and the shell in order to seal the opening in the body, through which the insulator extends, against escape of gases. The rear end of the igniter plug is generally welded in or brazed in several places to assure that there is a pressure-tight seal through which pressurized gases will not pass. The front end of the igniter plug includes an insulator which surrounds the central electrode and which isolates the central electrode from the outer shell. In operation, when a proper operating voltage is applied to the igniter plug electrodes, an arc is struck between the forward portion of the inner electrode and the forward portion of the outer shell which is the ground electrode.

After the igniter plug has been in use for sometime, the forward portion of the insulator, separating the inner electrode from the outer electrode, is eroded away and causes the insulator to become loose (rattle around). This condition creates an air gap between the insulator and the outer electrode which requires a higher voltage be applied between the electrodes to establish a discharge. At times, the power source supplying the voltage and the electrodes is inadequate to supply this additional voltage and the plug does not supply the necessary discharge to ignite fuel within an engine. For example, during certain operating modes of a jet aircraft, such as take-off, maximum climb and thrust reversal during landing. the firing end of the igniter plug is subject to high temperatures and pressures, which, together with an increased firing gap caused by spark erosion during service life, demand quite an increase in ionization voltage between the electrodes to maintain a discharge. Under these conditions, with the increased firing gap, the power supply, which generally has a rated maximum voltage and power, is incapable of supplying the voltage between the electrodes necessary to maintain an electric discharge to ignite fuel within the engine. A further problem associated with existing igniter plugs is that the forward insulator, separating the inner electrode from the outer electrode. is rigidly mounted between the two electrodes so that thermal expansion and contraction during operation sets up stresses on the insulaator which eventually lead to the cracking of the insulator and the failure of the igniter plug. One example of an igniter plug having the aforementioned problems may be found in US. Pat. No. 3.745.400 entitled lgniter Plug" and issued July 10, l973 to Helmut P. Meyer.

SUMMARY OF THE INVENTION This invention provides an igniter plug for a turbine engine that has a spring biased insulator between the two electrodes of the igniter plug that compensates for thermal expansion and erosion of one of the electrodes.

The invention is an improved igniter plug characterized by a spring 100 or 200 that applies an axial force on the insulator 80 that separates the inner electrodes from the outer electrode 20 so that the insulator 80 is always in contact with the electrodes 20 and 30.

In one embodiment of the invention, the improved igniter plug comprises: an inner elongated electrode 30 having a front portion and a rear portion; a forward elongated insulator 80 disposed around the forward portion of the electrode 30; an intermediate elongated insualtor disposed around at least the rear portion of the electrode 30, the intermediate insulator 40 hav ing a front portion and a rear portion; an outer elongated metal shell 20 disposed around the electrode 30 and electrically isolated therefrom by the forward and intermediate insulators 40 and 80, the metal shell 20 having a rear portion that has an opening therein and a front end portion 23 arranged to provide a spark gap with the end 32 of the front portion of the electrode 30; the rear portion of the elongated electrode 30, intermediate insulator 40 and shell 20 being completely welded and/or brazed to form a pressure-tight seal at the rear end of the igniter plug; and a spring 100 and/or 200 for axially biasing the forward insulator 80 against the forward portion 23 of the metal shell 20.

Accordingly, it is an object of this invention to provide an improved igniter plug that includes an axially biased internal insulator that moves in response to thermal expansion, contraction and/or wear.

It is a further object of this invention to provide an igniter plug that includes an internal insulator that is biased to maintain contact between the inner and outer electrodes over the life of the igniter plug.

It is still another object of this invention to eliminate the failure of internal insulators of igniter plugs due to thermal expansion and contraction between the insulator and an outer metal shell.

It is yet another object of this invention to bias the insulator that isolates the internal electrode from the em ternal electrode witout imposing excessive compressive stresses which crack the insulator when the igniter plug is subjected to thermal expansion and contraction during operation.

It is another object of this invention to increase the useful life of the igniter plugs.

Accordingly, the above and other objects and features of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings and claims which form a part of this specification.

DETAILED DESCRIPTION OF THE DRAWING The single FIGURE is a cross-sectional diagrammatic view of an igniter plug that incorporates the principles of this invention.

The igniter plug comprises an elongated central electrode 30; a ceramic insulator 40; a first metal dia phragm an outer metal shell 20, which forms the second electrode; a second diaphragm 10 concentrically arranged between the insulator 40 and the shell 20; a forward insulator and a bushing 60.

The central electrode 30 is generally comprised of an electrically conducting material so that when the cen tral electrode 30 is in electrical circuit relationship with the front portion 23 of the outer shell electrode 20, an arch discharge may be formed between the tip 32 of the electrode 30 and the surrounding portion 22 of the shell electrode 20. The forward end portion of electrode 30 from which the spark discharge occurs includes a cylindrically shaped end portion 32 that is of a much larger diameter than the rest of the electrode and which contains therein one or more passages 31 for the passage of gas to cool the tip 32 of the electrode 30 during operation.

Surrounding most of the central electrode 30 is a ceramic insulator 40 which electrically isolates the central electrode 30 from the outer shell electrode 20. To prevent any gases from escaping through the bore 41 of the insulator 40, a first diaphragm 50 connects (brazed) and seals in fluid-tight relationship the insulator 40 and the center electrode 30.

The first diaphragm 50 is generally comprised of a metallic material that is brazed to form a continuous 360 bond 51 between the first diaphragm 50 and a portion of the inside of the insulator 40. To assure a fluid-tight seal between the first diaphragm 50 and the center electrode 30, first diaphragm 50 is brazed to the center electrode to form a continuous 360 bond 52.

In accordance with standard igniter plug fabrication, a cylindrical copper wedge 60 is located between the outer shell 20 and the intermediate insulator 40.

The outer shell 20 includes a mounting flange 9 for mounting the igniter plug in a turbine engine; intake and exhaust ports 24, 26, 27, 28 for allowing the entrance and exit of engine gases in the igniter plug to cool the electrode 30; and a forward shell portion or cap 23, that is welded to the shell 20 at point 29 to form the entire outer electrode 20. The front portion of the shell cap 23 includes an opening 22 that forms the discharge surface of shell electrode 20 that, together with the discharge surface 32 of the control electrode 30, forms the discharge gap. When assembling the igniter plug, the last two pieces added to the assembly are the forward ceramic insulator 80 and then the cap shell 23, which is then welded to the shell 20 to retain the forward insulator 80 and inner electrode 30 in position.

The second diaphragm 10 is preferably a metallic material such as a nickel-iron alloy chosen for its resilient features over a wide range of temperatures to 700F.) and is concentrically arranged around the intermediate insulator 40. The forward portion of the diaphragm is brazed at 11 to the insulator 40 to form a continuous 360 bond between the insulator 40 and the second diaphragm 10. The opposite end of the diaphrgm is welded at 12 to the shell to form a continuous 360 bond between the diaphragm l and the shell 20. In the arrangement shown, the weld 12, connecting the diaphragm 10 to the shell 20, functions as a hinge to compensate for an increase in the radial distance, together with the rear end portion 2 of the diaphragm 10, between the outside of the insulator 40 and the inside of the shell 20.

A second forward ceramic insulator 80 having a shoulder 81 is also positioned within the shell 20 to prevent radial and axial movement of the control electrode that might result in contact between the control electrode 30 and the shell electrode 20; hence, preventing electrical short circuits. The forward ceramic insulator includes a rearwardly facing shoulder that together with a forwardly facing internal shoulder 25 of the outer shell 20 captivates spring which axially and resiliently biases the forward insulator 80 in the forward direction. During operation, when the forward portion of the igniter plug is subjected to thermal expansion and contraction, the spring 100 biasing the insulator 80 allows thermal contraction of the outer electrode 20 without cracking the insulator 80. Further, as the age of the igniter plug increases and the are discharge between the inner electrode forward tip 32 and the outer electrode surface 22, 21 wears away to expose surface 21, the spring 100 applies an axial force to the insulator 80 so that the insulator 80 will always be in presure contact with a portion of the surface 21 of the outer electrode. This continuous contact of the insulator 80 with a portion of the surface 21 pervents an air gap from occurring between the insulator 80 and the outer electrode 20 which results in improper operation of the igniter plug and/or failure of the igniter plug to ignite fuel in a turbine engine.

A second spring 200 may be compressedly captivated around the intermediate electrode 40 and between the bushing 60 and one end 86 of the forward insulator 80 to provide an axial force on the forward insulator 80 in the direction of the end 32 of the inner electrode 30.

The springs 100,200 are preferably made of material which has the capability to maintain a high yield strength when exposed to the hot operational environment of the igniter tip. Suitable materials include nickel base alloys such as inconel X-750 which exhibits a high yield strength at temperatures approaching l,O00F. or even higher,

While a preferred embodiment of the invention has been disclosed, it will become apparent to those skilled in the art that certain changes may be made to the invention as set forth in the appended claims and, in certain cases, certain features of the invention may be used to advantage without corresponding use of other features. For example, the axial force applied to the forward insulator 80 may be applied by only one spring 100 or 200 or by using both springs. Further, the axial force applied to the insulator may be accomplished by curved or wavy washers, although springs 100 or 200 are preferred. Accordingly, it is intended that the illustrative and descriptive materials herein be used to illustrate the principles of the invention and not to limit the scope thereof.

Having described the invention, what is claimed is:

1. In combination with a spark plug of the type having an inner elongated electrode having a front portion and a rear portion; a forward elongated insulator dis posed around the forward portion of said electrode, an intermediate elongated insulator disposed around at least the rear portion of said electrode, said intermediate insulator having a front portion and a rear portion; an outer elongated metal shell disposed around the electrode and electrically isolated therefrom by the forward and intermediate insulators, said metal shell having a rear portion that has an opening therein and a front end portion arranged to provide a spark gap with the end of the front portion of said electrode, said forward elongated insulator having its forward end immediately adjacent the spark gap, a first forward portion in contact with a portion of the front end of said outer elongated metal shell, and a second forward portion in contact with a portion of the front end of the inner elongated electrode whereby said forward elongated insulator extends adjacent said spark gap between said metal shell and inner electrode; and a metal sleeve having a front end portion that includes an opening that is in mated relationship with the rear portion of said intermediate insulator, the inside of said front end portion of said sleeve annularly fastened in pressure tight relationship to the outside rear portion of said intermediate insulator; and a rear end portion having a configuration that matches the opening in the rear of said metal shell. the rear end of said metal sleeve annularly fastened in pressure tight relationship to the rear end of said metal shell whereby said intermediate insulator and said shell are connected together by said sleeve, the improvement comprising:

means for slidably mounting said forward insulator, including means for axially and resiliently biasing said forward insulator against said front end portion of said shell.

2. The combination as recited in claim 1 wherein the means for biasing said insulator against said front end portion of said shell comprises:

a spring compressedly captivated between a rearward facing shoulder located on the outside of said forward insulator front portion and a forwardly facing shoulder located on the inside of said shell adjacent to and spaced from said forward insulator rearward facing shoulder.

3. The combination as recited in claim 1 wherein said means for biasing said forward insulator includes a spring compressedly captivated between the rear end of said forward insulator and stop means located in said metal shell.

4. The combination as recited in claim 1 wherein said means for biasing said forward insulator includes a spring disposed within said shell that applies an axial force to said forward insulator in the direction of the front portion of said shell.

5. In combination with a spark plug of the type having an inner elongated electrode having a front portion and a rear portion; an elongated insulator means disposed around at least a portion of the electrode, said insulator means having a front portion and a rear portion; an outer elongated metal shell disposed around the electrode and electrically isolated therefrom by said insulator means, said metal shell having a rear portion and a front portion arranged to provide a spark gap with the end of the front portion of said electrode; the front end of said insulator means having a surface, disposed adjacent the spark gap, that extends from the front portion of said metal shell to the front portion of said inner elongated electrode; and means for providing an annular pressure-tight seal between the rear portions of said center electrode, said insulator and said shell, the improvement comprising:

means for slidably mounting said insulator means, in-

cluding means for axially biasing said elongated insulator means against said front end portion of said metal shell.

6. The combination recited in claim 5 wherein the means for biasing said elongated insulator means against the front end portion of said shell comprises:

a spring.

7. The combination recited in claim 6 wherein said spring is compressedly captivated between a rearwardly facing shoulder located on the outside of said elongated insulator front portion and a forwardly facing shoulder located on the inside of the front portion of said shell adjacent to and spaced from said insulator rearwardly facing shoulder.

8. The combination as recited in claim 6 wherein said spring is within said shell and exerts an axial force on said insulator means in the direction of the front portion of said electrode. 

1. In combination with a spark plug of the type having an inner elongated electrode having a front portion and a rear portion; a forward elongated insulator disposed around the forward portion of said electrode; an intermediate elongated insulator disposed around at least the rear portion of said electrode, said intermediate insulator having a front portion and a rear portion; an outer elongated metal shell disposed around the electrode and electrically isolated therefrom by the forward and intermediate insulators, said metal shell having a rear portion that has an opening therein and a front end portion arranged to provide a spark gap with the end of the front portion of said electrode, said forward elongated insulator having its forward end immediately adjacent the spark gap, a first forward portion in contact with a portion of the front end of said outer elongated metal shell, and a second forward portion in contact with a portion of the front end of the inner elongated electrode whereby said forward elongated insulator extends adjacent said spark gap between said metal shell and inner electrode; and a metal sleeve having a front end portion that includes an opening that is in mated relationship with the rear portion of said intermediate insulator, the inside of said front end portion of said sleeve annularly fastened in pressure tight relationship to the outside rear portion of said intermediate insulator; and a rear end portion having a configuration that matches the opening in the rear of said metal shell, the rear end of said metal sleeve annularly fastened in pressure tight relationship to the rear end of said metal shell whereby said intermediate insulator and said shell are connected together by said sleeve, the improvement comprising: means for slidably mounting said forward insulator, including means for axially and resiliently biasing said forward insulator against said front end portion of said shell.
 2. The combination as recited in cLaim 1 wherein the means for biasing said insulator against said front end portion of said shell comprises: a spring compressedly captivated between a rearward facing shoulder located on the outside of said forward insulator front portion and a forwardly facing shoulder located on the inside of said shell adjacent to and spaced from said forward insulator rearward facing shoulder.
 3. The combination as recited in claim 1 wherein said means for biasing said forward insulator includes a spring compressedly captivated between the rear end of said forward insulator and stop means located in said metal shell.
 4. The combination as recited in claim 1 wherein said means for biasing said forward insulator includes a spring disposed within said shell that applies an axial force to said forward insulator in the direction of the front portion of said shell.
 5. In combination with a spark plug of the type having an inner elongated electrode having a front portion and a rear portion; an elongated insulator means disposed around at least a portion of the electrode, said insulator means having a front portion and a rear portion; an outer elongated metal shell disposed around the electrode and electrically isolated therefrom by said insulator means, said metal shell having a rear portion and a front portion arranged to provide a spark gap with the end of the front portion of said electrode; the front end of said insulator means having a surface, disposed adjacent the spark gap, that extends from the front portion of said metal shell to the front portion of said inner elongated electrode; and means for providing an annular pressure-tight seal between the rear portions of said center electrode, said insulator and said shell, the improvement comprising: means for slidably mounting said insulator means, including means for axially biasing said elongated insulator means against said front end portion of said metal shell.
 6. The combination recited in claim 5 wherein the means for biasing said elongated insulator means against the front end portion of said shell comprises: a spring.
 7. The combination recited in claim 6 wherein said spring is compressedly captivated between a rearwardly facing shoulder located on the outside of said elongated insulator front portion and a forwardly facing shoulder located on the inside of the front portion of said shell adjacent to and spaced from said insulator rearwardly facing shoulder.
 8. The combination as recited in claim 6 wherein said spring is within said shell and exerts an axial force on said insulator means in the direction of the front portion of said electrode. 